This invention relates to an apparatus for estimating a neutral position for the steering handle of a motor vehicle. Although the invention will be described in connection with a rear wheel steering control system, it should be understood that the invention is equally applicable to other vehicle dynamic characteristic control systems including active suspension control systems and the like utilizing information on steering wheel position to control the vehicle dynamic characteristics including yaw velocity, side velocity, roll velocity, etc.
For example, Japanese Patent Kokai No. 59-26341 discloses a steering handle neutral position estimating apparatus which employs a steering handle position sensor for sensing the existing steering handle position. The existing steering handle position is set for a steering handle neutral position when two conditions are fulfilled; that is, when the existing steering handle position is within a predetermined range, and when vehicle has traveled from the rest at a distance greater than a reference value. The steering handle neutral position estimating apparatus can estimate the steering handle neutral position with high accuracy by increasing the reference value with increasing traveling distance. Since the estimated steering handle neutral position is held until the two conditions are fulfilled again, however, it takes a long time to cancel an erroneous steering handle neutral position which may be set because of a failure in the steering handle position sensor or a high speed operation of the steering handle. This is true particularly with steering handle neutral position estimating apparatus of the type having such conditions which becomes more severe as the traveling distance increases.